Of 19,413 high school football players that were studied, the incidences of head and neck injury were found to be 1.0% and 0.6% respectively. Comparison with results of a 1948 study revealed a decrease in head injury incidence of 57% since that time. This reduction corresponds with the more widespread use of the hardshell plastic helmet and the double-bar faceguard. Factors producing injury in 182 head and neck injuries studied included improper fitting of headgear, the practice of "spearing," violations of basic fundamentals of football play, and inadequate physical conditioning. The vast majority of neck injuries were sustained in flexion, and the faceguard was found not culpable in the production of those injuries. Efforts to cause helmets to impinge on the posterior neck during hyperextension were unsuccessful when helmets were properly fitted.
Alley RH. Head and Neck Injuries in High School Football. JAMA. 1964;188(5):418-422. doi:10.1001/jama.1964.03060310018004